Location Based Services (LBS), known as mobile location services or location services, enable a mobile network to acquire the geographical position information (that is, latitude and longitude coordinates) of a mobile terminal using a specific locating technology, provide the acquired geographical position information to a mobile terminal user, a communication system or a third party, and provide, with the support from certain electronic map information, the mobile terminal user with calls or non-call services related to the position of the mobile terminal user.
The location manners of a mobile communication network comprise a cell-based location, a location based on conventional Global Positioning System (GPS) and an Assisted GPS (AGPS) location, wherein the AGPS location is a location technology which combines the GPS location with a mobile communication system and has been widely applied owing to its quick positioning speed and high positioning accuracy.
Currently, in the Secure User Plane Location (SUPL) protocol of Open Mobile Alliance (OMA), the location flow initiated by a terminal comprises the following steps:
step 1: an AGPS location application program on the terminal is connected with a location services apparatus of the AGPS via a packet data domain to send an SUPL START message to request a location;
step 2: the location services apparatus searches, via the cell identifier (CELL ID) information included in the SUPL START message, a base station database (used for storing a cell identifier and the cell position information corresponding to the cell identifier) for the position information of the cell where the terminal resides so as to acquire the current rough position of the terminal, calculates assistance data with the rough position in combination with its own GPS reference information, and sends the calculated assistance data to the terminal; and
step 3: the terminal captures a GPS satellite signal according to the received GPS assistance information and carries out a location quickly. The specific location method may be understood by reference to an Open Mobile Alliance-Technology Specification-User Plane Location Protocol (OMA-TS-ULP).
A cell-based location flow comprises the following steps:
step 1: a location Service Provider (SP) sends a locating request to a location service apparatus to request it to locate a terminal;
step 2: after receiving the request, the location service apparatus sends a locating request to a Home Location Register (HLR), and the HLR returns the cell information of the terminal;
step 3: after receiving the cell information of the terminal, the location service apparatus searches a base station database for the position of the cell where the terminal resides; and
step 4: the location service apparatus sends the position of the cell where the terminal resides to the service provider.
The location flows above both need to search a base station database for the position of the cell where a terminal currently resides, however, it is a hard task for the base station database to acquire the position information of all the cells of the worldwide mobile networks and update the information timely and accurately. Acquiring a correct cell position is impossible when a terminal is in a roaming state (meaning that the position information of the cell where the terminal resides cannot be found in the base station database) and the base station database stores no information of the base station where the terminal is roaming, leading to a failed location. Therefore, it is impossible to locate the cell where a roaming terminal resides.